|Quadrangle map, 1:250,000-scale||SR|
|Quadrangle map, 1:63,360-scale||D-3|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is at an elevation of about 1,500 feet, on the south side of the divide between Derickson Bay and Squaw Bay. It is in the NW1/4 section 22, T. 9 N., R. 9 E., of the Seward Meridian. This is location 165 of Tysdal (1978 [MF-880-A]) and location S-122 of Jansons and others (1984) and is accurate to within a quarter of a mile.|
Geologic descriptionThe Gray Brothers prospect is near the Contact Fault, which separates sedimentary rocks of the Valdez Group of Late Cretaceous age from sedimentary rocks of the Orca Group of early Tertiary age (Cobb and Tysdal, 1980). The deposit is a sulfide-bearing quartz vein in a shear zone in green-gray slate and phyllite of the Valdez Group. The shear zone is 10 to 20 feet wide; it strikes N 30 E and dips vertically. The vein is exposed for about 1,000 feet along strike and pinches and swells from 2 inches to 10 feet in width. Pyrite, arsenopyrite, and pyrrhotite have been identified in the vein, but overall, it contains very sparse sulfides. Seven samples collected by the U.S. Bureau of Mines in 1979 contained as much as 1,100 ppm arsenic and less than 1 ppm gold (Hoekzema and Sherman, 1983). Workings consist of a 40-foot adit at 1,550 feet elevation, a 15-foot trench at 1,750 feet, and various prospect pits.
|Geologic map unit||(-147.841772189177, 60.8578713146734)|
|Mineral deposit model||Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)|
|Mineral deposit model number||36a|
|Age of mineralization||Oligocene or younger; the Contact Fault cuts Oligocene granitic rocks northeast of the prospect.|
|Workings or exploration||The prospect was discovered in 1913 by the Gray Bothers, who developed a 40-foot adit at 1,550 feet elevation, a 15-foot trench at 1,750 foot elevation and various prospect pits (Johnson 1914 [B 592-G, map p. 196 only mention]). Seven samples collected by the U.S. Bureau of Mines in 1979 contained as much as 1,100 ppm arsenic and less than 1 ppm gold (Hoekzema and Sherman, 1983).|
|Indication of production||None|
Additional commentsThe U.S. Bureau of mines reported three cases of dynamite in the adit in 1979 (Hoekzema and Sherman, 1983).
Cobb, E.H., and Tysdal, R.G., 1980, Summaries of data on and list of references to metallic and selected nonmetallic mineral deposits in the Blying Sound and Seward quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-621, 276 p.
Condon, W.H., and Cass, J.T., 1958, Map of a part of the Prince William Sound area, Alaska, showing linear geologic features as shown on aerial photographs: U.S. Geological Survey Miscellaneous Investigations Series Map I-273, 1 sheet, scale 1:125,000.
Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000.
Johnson, B.L., 1914, The Port Wells gold-lode district, Alaska: U.S. Geological Survey Bulletin 592-G, p. 195-236.
MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.
|Reporters||Jeff A. Huber (Anchorage)|
|Last report date||12/31/1999|